The up button is truncated when set the DateTimePicker’s ShowUpDown property to True

* .NET Core Version:
5.0.100-rc.1.20367.2

* Have you experienced this same bug with .NET Framework?:
Yes

**Problem description:**
After set the ShowUpDown property of dateTimePicker to True, then observe the up/down buttons, you'll find the up button is truncated.

**Expected behavior:**
It shouldn’t be truncated.

**Minimal repro:**
1. Create a winforms core project.
2. Drag and drop a dateTimePicker control.
3. Set its ShowUpDown property to True.
4. Build and run the project.
5. Observer the Up/Down buttons.

Or run the attached project: [ShowUpDown.zip](https://github.com/dotnet/winforms/files/4969905/ShowUpDown.zip)